The present invention relates to methods used for producing camshafts of internal-combustion engines, of the type in which a metal tubular element is expanded by introducing a high-pressure fluid therein. A method of this type is, for example, described and illustrated in the document No. WO 2003/033189. According to the above known technique, the camshaft is obtained by mounting a series of annular elements that are to define the cams on a tubular element and by expanding the tubular element with a hydroforming operation in order to secure the aforesaid annular elements to the tubular element. There are on the other hand known alternative methods of production in which the annular elements defining the cams are secured to the tubular element by expanding the latter by means of a mechanical action, with the aid of an expansion mandrel. The known methods described above have been proposed and used as an alternative to more conventional methods, which envisage obtaining a camshaft in a single piece, by means of a conventional forging operation.
A method as set forth in the preamble of claim 1 is known from WO 99/20414 A1. Similar methods are known from JP 2000 192805 A, EP 0 906 800 A1, US 2003/221514 A1, JP S59 113944 A.
The object of the present invention is to provide a camshaft for an internal-combustion engine by means of a forming operation using high-pressure fluid, in particular by hydroforming or by forming with gas at a high pressure to obtain at the same time a camshaft structure in a single piece.
With a view to achieving the above purpose, the subject of the invention is a method having the features of claim 1.